So the Pearsons aren't as perfect as you thought. This Is Us showed Jack (Milo Ventimiglia) and Rebecca (Mandy Moore ) in their first big fight in the Tuesday, Feb. 14 episode titled "Jack Pearson's Son." What happened? Rebecca never disclosed the fact that she was in a band with her former boyfriend. The band that she was going to on a five-state tour with, leaving Jack and her kids behind. Jack was supportive, at first, until he found out the ex-boyfriend factor.

The fight, on Valentine's Day of all days, brought up some feelings that have been festering. See the big moment below.

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"These are issues that have been boiling for a while," Moore said on the This Is Us after show. "And Milo and I talked a lot about it. I don't think this is a couple that fights often at all. I think that they have a very open line of with one another."

Which is what makes the confrontation so shocking. Rebecca told Jack his jealousy gets out of control and she needed to have something for herself without Jack getting in her way. By the time of the fight, 1996, Jack and Rebecca have been together roughly 20 years, obviously not in the same place they once were.

"And I believe that there is a lot of resentment that's just been building for years, about, from my perspective as a woman, this is a woman who had a sort of trajectory that she was on, that she saw for herself, her life and her career. She met Jack, fell in love, kind of tabled all of that, tabled who she was fundamentally, like a huge piece of who she was, as an artist and as a creative person," Moore said. "Didn't know whether or not she wanted to have kids, was sort of on the fence. That happened. Cut to 16 years later, the possibility of that entering her life again is so equal parts exciting and thrilling, but also terrifying."

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Moore said the fact that her enjoyment has been met with some "semblance of resistance from the beginning, from Jack, that he couldn't let her have that is really disheartening."

But Ventimiglia feels like from Jack's perspective, he "doesn't like change, doesn't care for change."

"So, having a routine of so many years, of having the kids and just the possible repetitive nature of things, he enjoys it," Ventimiglia said. "He loves it." So even the smallest twist, like the divorce of his friends, throws him for a loop.

"Again, I always go back to Jack feels like a very simple person…very black and white," he said.

"There's not a lot of nuance," Moore added.

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After the fight, Jack went to the restaurant he was supposed to take Rebecca to and had his first drink in years. Yes, after he promised to quit drinking for his family all those years ago. "Jack's very black and white, easy wave experiencing things and hearing things," Ventimiglia said. So hearing his wife tell him he's held her back clicks for him. "I think also, in a very linear kind of way, what his wife wanted was to spend time with another man," Ventimiglia tried to explain.

"That's not rational," Moore interjected. She said it was "cruel" that Jack leaves, but notes they needed space. Ventimiglia said Jack left knowing he was going to have a drink.

Find out where it all leads when This Is Us airs Tuesdays, 9 p.m. on NBC.